Not sure what kind of rock these are but if they look familiar to anyone I would like to know. I use them as a little cave. The rock in the first pic has shiny little bits in it. One, or all, of them seem to have a PH buffering quality as my tap water runs at 8.0 and my tank water is at about 6.4 - 6.6 except right after a PWC, then it is about 6.8.
Please forgive the ugly blue clown puke gravel. Considering changing it this week to prepare for a mass planting.
Thanks for your time.